In an effort to improve consistency between ROS 1 and ROS 2 docker images, we now have `ros_core`, `ros_base` and `desktop` "metapackages" in ROS 2 (Bouncy and Ardent).

As a result the ROS 2 docker images are now named as follows:
- `osrf/ros2:ardent-ros-core`
- `osrf/ros2:ardent-ros-base`
- `osrf/ros2:ardent-desktop`
- `osrf/ros2:bouncy-ros-core`
- `osrf/ros2:bouncy-ros-base`
- `osrf/ros2:bouncy-desktop`

We are planning on purging the previous images on Monday 2018-08-06.
This will result in the following:
- ROS 2 beta images (r2b2, r2b3) will not be available anymore
- Ardent and Bouncy images will only be available with the new names listed above.